This invention relates to a master information carrier used for static and areal lump-sum recording of digital information signals on a magnetic recording medium, and a magnetic recording method using the same.
A magnetic reading and reproducing apparatus has seen increases in recording density to achieve a small size and large capacity. Especially, in the field of a hard disk drive as a typical magnetic recording device, an areal recording density of more than 3 Gbit/in2 is already available on the market. Furthermore an areal recording density of 10 Gbit/in2 is expected in a few years, when the rapid technical advance is taken into consideration.
One of the primary technical factors that has enabled such high recording density is the increasing linear recording density, due to improvements of medium properties, a head-disk interface performance, and new signal processing methods such as partial response. Recently however, the rate of increase in track density exceeds considerably that of linear recording density, and thus becomes a primary factor of the increasing areal recording density. Practical use of a magneto-resistive type head, which is superior to a conventional inductive type head in reproduction output performance, has contributed to the progress in the track density. It is possible at present to read a signal from a track whose width is at most only a few microns with good S/N ratio by practical use of the magneto-resistive type head. Further it is expected that the track pitch will reach the sub-micron range in the near future along with further improvement of the head performance.
A tracking servo technique is important for the head to read a signal with high S/N ratio by scanning precisely such a narrow track. A conventional hard disk has areas that are located at predetermined angular intervals around the disk over 360 degrees and in which information such as a tracking servo signal, an address signal and a read clock signal are recorded (hereinafter, recording such signals is referred to as xe2x80x98preformatxe2x80x99). A magnetic head can scan a track by reading such information at predetermined periods, and monitoring and correcting the head position.
The above-mentioned tracking servo signal, an address and a read clock signal are to be reference signals for the head to scan a track precisely. Therefore, precise record positions are required for these information signals. Current preformat recording into a hard disk is performed precisely by magnetic heads that are precisely position-controlled in a special servo-track recording apparatus after installing the disk into the drive.
The above-mentioned preformat recording of a servo signal, an address signal and a read clock signal using the magnetic head in such a special servo-track recording apparatus has some problems as follows.
The first problem is due to the fact that the relative movement between the head and the medium is necessary in general for recording with the magnetic head. This fact means that a substantially long period is required for preformat recording in the above-mentioned method while controlling precisely the positions of the head, using a special servo-track recording apparatus. In addition, the special servo-track recording apparatus is expensive. Thus, the cost for preformat recording is quite high.
The second problem is that due to a space between the head and a medium or due to a diffusive recording magnetic field caused by a pole shape of the recording head, the magnetic transition at track edges of the recorded preformat signals lacks steepness. In a current tracking servo technique, the head position is detected by the amount of a change in a read signal amplitude when the head misses a track. Therefore, the system requires a steep off-track performance, in which reproduced read signal amplitude changes sharply as the head misses the track. The diffusive recording magnetic field is contrary to this requirement, and thus, makes it difficult to realize a precise tracking servo technique that is required for a sub-micron track recording.
In order to solve the above-mentioned problems in preformat recording with a magnetic head, the inventors disclose a new preformat recording technique in Unexamined Published Japanese Patent Application (Tokkai Hei) 10-40544. The reference discloses a master information carrier having a shape pattern corresponding to an information signal array, and the pattern is provided as an array of a ferromagnetic material deposited on a nonmagnetic substrate surface. The master information carrier surface is brought into secure contact with a magnetic recording medium surface, so that a magnetic pattern corresponding to the pattern array of the ferromagnetic material on the master information carrier is recorded on the magnetic recording medium.
According to the disclosure of Tokkai-Hei 10-40544, the ferromagnetic material composing the master information carrier surface is magnetized in a direction. Due to the recording magnetic field generated by this ferromagnetic material, a magnetization pattern corresponding to the pattern array of the ferromagnetic material of the master information carrier is recorded on a magnetic recording medium. That is, the preformat recording of a tracking servo signal, an address signal, a read clock signal and other signals is achieved by using the corresponding pattern array formed on the surface of the master information carrier.
While relative movement between the head and the medium is required for conventional linear recording with a head, Tokkai-Hei 10-40544 is characterized by a static and areal lump-sum recording that does not require relative movement between a master information carrier and a medium. As a result, the technique disclosed in Tokkai-Hei 10-40544 is generally effective for the problems related to preformat recording as follows.
First, since areal recording is carried out in Tokkai-Hei 10-40544, the time needed for the preformat recording is substantially shorter as compared to the prior art using a magnetic head. In addition, an expensive servo-track recording apparatus for precise position control of the magnetic head is not necessary. Therefore, the technique disclosed in the reference can improve the productivity of the preformat recording and reduce production costs.
Secondly, a space gap between the master information carrier and the magnetic recording medium can be minimized by bringing the surface of the master information carrier into secure contact with the surface of the magnetic recording medium, since relative movement between them is not required for the static recording. In addition, unlike the prior art using a magnetic head, a diffusive recording magnetic field caused by a pole shape of the magnetic head does not occur. Thus, the magnetic transition at track edges of the recorded preformat signal is steeper compared with the recording with a magnetic head. This further ensures precise tracking.
The magnetic recording technique disclosed in Tokkai-Hei 10-40544, however, cannot provide a structure which is maximized in view of the magnetic recording performance.
For example, in the magnetic recording technique disclosed in Tokkai-Hei 10-40544, magnetic properties of ferromagnetic materials on the master information carrier surface greatly affect the magnetic recording performance. Tokkai-Hei 10-40544 has some disclosure about the magnetic properties of the ferromagnetic materials suitable for the magnetic recording technique in the range clarified at the application. The application, however, has not clarified particularly-preferred properties that allow the best recording performance in the magnetic recording technique.
The magnetic recording technique disclosed in Tokkai-Hei 10-40544 is a new magnetic recording technique having a magnetic recording mechanism that is completely different from that of a conventional technique, and thus, it is difficult to obtain the master information carrier structure with superior magnetic recording performance and a preferred magnetic recording method by analogy with the prior art.
In the magnetic recording technique, therefore, sufficient experiments are required to clarify the magnetic recording mechanism, and early provision of a master information carrier with superior magnetic recording performance and a method of magnetic recording using the same based on the clarified mechanism are required.
In view of the above problems, this invention seeks to provide a master information carrier with sufficiently good magnetic recording performance, and a preferable magnetic recording method using the master information carrier.
The inventors studied energetically the magnetic recording technique focusing on the disclosure of Tokkai-Hei 10-40544 to develop the mechanism regarding the magnetic recording performance, and reached a structure of a master information carrier to obtain superior recording performance and a magnetic recording method using the same.
For the above-mentioned purposes, a master information carrier of this invention comprises a shape pattern corresponding to an information signal array to be recorded on a magnetic recording medium, which is provided by an array of a ferromagnetic thin film deposited on a nonmagnetic substrate. The ferromagnetic thin film is a soft magnetic film or a semihard magnetic film in which the coercive force in the track length direction of the information signal is not more than 40 kA/m, and the residual magnetization of the ferromagnetic thin film in the track length direction of the information signals is greater than the coercive force of the magnetic recording medium. Preferably the ferromagnetic thin film has a saturation magnetization at least three times the coercive force of the magnetic recording medium, and further preferably, it has at least 100 relative permeability in the length direction of the information track.
In a magnetic recording method using the above-mentioned master information carrier, magnetization information corresponding to an information signal array is recorded on a magnetic recording medium by bringing the master information carrier into secure contact with the magnetic recording medium surface and by applying a direct current (dc) excitation magnetic field to excite the ferromagnetic thin film, wherein the master information carrier has a shape pattern corresponding to the information signal array by arraying a ferromagnetic thin film deposited on a nonmagnetic substrate. The dc excitation magnetic field is not more than the coercive force of the magnetic recording medium, and magnetization residing in the ferromagnetic thin film after eliminating the dc excitation magnetic field is greater than the coercive force of the magnetic recording medium. The dc excitation magnetic field is preferably smaller than the saturation magnetic field of the ferromagnetic thin film.
Accordingly, this invention can provide, in a magnetic recording technique based on the disclosure of Tokkai-Hei 10-40544, a master information carrier having better magnetic recording performance and a magnetic recording method using the master information carrier.